In order to make a closed plastic bottle filled with a liquid or fluent material, one normally starts with a thermoplastic strip that is heated to its softening point and shaped, for instance by deep-drawing, into a row of receptacles of the desired shape. Alternately the softened portion of the strip can be deformed between a piston and die as described in U.S. Pat. Nos. 3,954,374 and 3,964,237 to create the desired shape.
Normally the starting-material strip of thermoplastic material is advanced in steps through the thermoforming device. It is unrolled from a large spool and is held along its edges over a space several millimeters wide both to advance it and hold it in place during the thermoforming operation. As a result the apparatus for unwinding and transporting the strip is cumbersome and complex, and the finished product must be trimmed, wasting from 5% to 30% of the material.
In addition to the conveying and waste problems, the use of a thermoplastic strip to form the receptacles has several other disadvantages. As a result of the shrinkage inevitably caused by the thermoforming operation, the band creeps and it is impossible to establish an accurate spacing between adjacent receptacles formed in the strip. Such inaccurate positioning is particularly troublesome when the joined-together receptacles are fed to an automatic filling, capping, and sealing system, since they will not be properly aligned. Thus the seal line for a cap will be misplaced laterally and, when the cap is subsequently trimmed, this seal line will be cut to create a leakage problem. Furthermore even if the seal line is not cut, the guillotine-style cutter normally used will exert considerable twisting forces on the receptacles if they are not cut in a perfectly flat area between receptacles, which twisting forces can open up the seal and ruin the product.
Furthermore in order to reduce wastage of the material from which the receptacles are made the pistons used for thermoforming are placed as closely as possible next to one another. This makes the equipment very dense and complex, and also makes it difficult to apply labels or otherwise act on the finished receptacles which are very close to one another. Similarly the devices that apply labels or other decoration or product identification to the closely spaced receptacles are fairly complex and expensive. What is more, when the filling operation directly follows the thermoforming operation, the receptacles must be formed to be open upward, in which position they can collect powder so the equipment must operate in a sealed so-called clean room to avoid dust and the like from collecting in the upwardly open receptacles.
In French patent 1,486,659 the receptacles are formed not from a strip but from plastic material injected as a powder or particles into a mold that is heated to melt the plastic and form the receptacle, with the mold subsequently moving along with the receptacle through the production line. The receptacles thus produced are therefore completely separate so the machinery is simplified but since the bases of the molds are closed subsequently operations are complicated. In particular only blow-molding or deep-drawing can be used which can result in nonuniform thickness in the finished receptacle. In addition only relatively shallow receptacles can be made by this method, and the production rate is invariably quite low. Such a system cannot conveniently be integrated with a filling and capping machine so that keeping them sufficiently clean for use, for instance, to package food becomes difficult.